The goal of this clinical trial is to assess whether a peri-operative intervention with nutritional immune modulating intervention (Ensure Surgery Immunonutrition shake) has beneficial effects on the complex interplay between gut microbiome, systemic inflammation and malnutrition that is commonly present in advanced heart failure and the adverse events associated with left ventricular assist device (LVAD) placement in hospitalized advanced heart failure patients awaiting LVAD implantation. The main questions it aims to answer are:

• Will pre-surgical supplementation with Ensure Surgery affect gut microbial composition and levels of inflammation among heart failure patients undergoing LVAD implantation?
• Will pre-surgical supplementation with Ensure Surgery affect post-surgical morbidity (e.g., infections, intensive care unit length of stay (LOS)) and mortality? Participants will be evaluated for malnutrition and will be given Ensure Surgery Immunonutrition shake to drink in the days preceding their LVAD surgery. Blood and stool samples will be collected at prespecified timepoints before and after surgery.

Researchers will compare malnourished participants drinking Ensure Surgery 3/day with well-nourished participants randomized to drink either 1/day or 3/day to see if any of the above supplementation strategies change the gut microbial composition, levels of inflammation, and post-surgical morbidity and mortality.

Heart failure (HF) has an estimated prevalence of >37.7 million individuals globally. In the US alone, which is projected to increase by 46% between the years 2012 and 2030. Despite significant advances in HF medical and device therapies, patient prognosis after their first HF hospital admission is poor, with a <50% survival rate at five years and significant proportion of patients progressing from chronic stable disease to advanced HF state. Once advanced HF ensues, LVADs are one of the two main treatment modalities that can meaningfully improve survival in this patient population.

Chronic systemic inflammation is commonly observed in HF and is believed to be directly related to its pathogenesis. Recently, perturbations in the gut microbiota known as "gut dysbiosis" and impairment of gut mucosal barriers, facilitating entry of endotoxins and gut metabolites into the circulation, have also been observed in HF patients. Elevated levels of circulating endotoxins and bacterial bi-products enhance systemic inflammation, thereby contributing to progression of HF to more advanced disease state. Gut microbial perturbations may also alter enterocyte structure and function resulting in gastrointestinal dysmotility, nutrient malabsorption and eventually malnutrition.

Malnutrition is frequent in HF (as high as 62%), is associated with higher rates of mortality, hospital readmissions and an increased risk of adverse early postoperative outcomes. Infections are the most common complications following LVAD, affecting >50% of HF patients, contributing significantly to postoperative mortality, increased length-of stay (LOS) and hospital readmissions. The pre-operative period may represent an attractive time window in which to optimize HF patients, correct deficiencies, and enhance immune defense mechanisms before surgery. This period allows to act upon modifiable risk factors, such as the nutritional status, and potentially lower the risk of postoperative complications. However, the literature on perioperative optimization in HF comes mainly from anesthesiology and focuses on intra- and immediate postoperative management, when it may be too late to intervene and alter the outcome. Interestingly, guidelines on the nutritional evaluation and management of patients prior to non-cardiac surgery are available, but very limited literature is published concerning cardiac surgery, and no data exists with respect to LVAD surgery. The investigators plan to evaluation of the impact of preoperative nutrition intervention.

Inclusion Criteria:

• age >18 years
• hospitalized
• undergoing LVAD therapy (enrolled at time of acceptance)

Exclusion Criteria:

• intubated
• congenital heart disease
• infiltrative cardiomyopathy
• unable to tolerate oral nutrition
• surgery expected in <5 days